Check valves are commonly used in numerous military and aerospace operations where dependable sealing and operating functions are required under demanding conditions. In typical check valves, a spring loaded valve member is located on a common longitudinal axis in a valve body or valve housing between an inlet port and an outlet port. A floating "O" ring seal on the valve member can be disposed between a metal sealing surface on the valve member and a valve seat in the valve body to cushion closing of the valve and to insure perfect sealing. Fluid under pressure in the inlet port will push the valve member to an open position when the pressure exceeds or overcomes the closing force of the spring acting on the valve member and flow in one direction through the valve. In the absence of sufficient pressure in the inlet port or a fluid pressure causing a fluid flow in a reverse direction, the closing force of the spring moves the valve member to a closed condition where the "O" ring seal prevents fluid flow. The valve member is arranged relative to the valve housing to compress the "O" ring sufficiently to engage the metal sealing surfaces of the valve member and the valve body. The valve member is arranged to have a metal-to-metal contact with the valve housing to prevent extrusion of the "O" ring with an excess pressure differential in a reverse direction. The valve member also has a longitudinally extending guide extension slidably received in a guide bore in the valve housing to guide the valve member for motion along the longitudinal axis of the valve housing when the valve member moves between an open and a closed condition.
Because of the spring and the mass of the valve member, certain flow velocities of fluid though the valve can cause a harmonic motion of the valve member which occurs at a natural frequency of the valve member. Over a period of time, such a harmonic motion accelerates the wear of the guide extension in the guide bore. The wear, in turn, leads to valve failure. This is a common effect in gaseous fluid service and can ruin a valve in a matter of hours in some instances.
The harmonic motion of a valve member can also introduce an undesirable disturbance in the consistency of fluid flow through the valve.
The wear of the guide extension and the guide bore also increases the clearance space between these two parts so that the valve member can tip or wobble about its longitudinal axis. This action accelerates the wear on the guide extension and the guide bore and can ultimately cause the valve member to jam thus fail.
The accelerated wear of a valve member also can cause particulate matter to be generated and introduced into the fluid flow which can be deleterious where fluid contaminates are not tolerated.
Thus, a check valve can have regions of operating instability which a user must avoid because the vibration of the valve element during operation.
In pressure regulators sometimes a damper is incorporated in the form of a bellows-sealed chamber that breathes through one or more orifices as it is forced to change volume by motion of the valve member. In this type of system, the bellows is not very effective for damping and has a limited life. Small breather orifices are also subject to contamination or plugging in use.